Good Day,

I have made 7 number of 555 timer astable multivibrators on 7 different perfboards with the following circuit to each give output of 0.1, 7, 14, 28, 35 and 42 Hz Frequencies.

Here are the values of resistance and capacitance I used for these frequencies.

0.1 Hz:
Ra = 5.5 kOhm
Rb = 719 kOhm
C = 10 uF

7 Hz:
Ra = 5.5 kOhm
Rb = 1021000 Ohm
C = 0.1 uF

14 Hz:
Ra = 5.5 kOhm
Rb = 510 kOhm
C = 0.1 uF

21 Hz:
Ra = 5.5 kOhm
Rb = 340 kOhm
C = 0.1 uF

28 Hz:
Ra = 5.5 kOhm
Rb = 254.5 kOhm
C = 0.1 uF

35 Hz:
Ra = 5.5 kOhm
Rb = 203 kOhm
C = 0.1 uF

42 Hz:
Ra = 5.5 kOhm
Rb = 169 kOhm
C = 0.1 uF

I made it all and I was finally testing the output voltages on no load. When I tested the 0.1 Hz circuit, initially at Vcc of 12 Volts DC, the voltage between output pin and ground was 11.9 Volts. The voltage was going up and down between 0 and 11.9 Volts every 5 seconds.

Now I tested the 14 Hz circuit. Initially the voltage between output and ground was 5.3 Volts. Then after a few minutes I saw that this voltage go to 11.9 Volts and it stayed there. Whenever I measure it shows 11.9 volts.

Then I tested the 42 Hz frequency circuit. Same as the 14 Hz, initially it showed 5.3 V between output and ground and suddenly after a few minutes it shows 11.9 Volts output and it stays there even if I power off and on multiple times.

Now I have three circuits - 0.1 Hz, 14 Hz and 42 Hz giving an output pulsating Voltage of 11.9 Volts.

Then I tested all the other four circuits with 7 Hz, 21 Hz, 28 Hz and 35 Hz. Initially they showed 5.3 Volts output but they never went up to 11.9 Volts as in the above cases. Two of them went up to 6.9 Volts and stayed there.

So I need some help I am confused and I cannot figure out why this happens. I thought it was the discharging capacitor, I tried discharging it but still I couldnt get it all to give more or less equal voltage output. When I try measuring voltages between the pins for very long, it fries up the 555 timer IC and I lost 3 of them.

Thanks.

 

When I try measuring voltages between the pins for very long, it fries up the 555 timer IC and I lost 3 of them

Hi sab,
This suggests a problem with the test meter, what type of meter are you using?
E

 

Hi sab,
This suggests a problem with the test meter, what type of meter are you using?
E

May be yes I am using a low cost pocket multimeter.

Now I checked the 28 Hz circuit. It was giving out 2.5 Volts output. I changed the 555 timer and it shows 5.3 Volts.

I am confused on this. As you suggest I should use a different multimeter and try it out.

 

Hi sab,
I would try a different test meter of known specification, let's know how it goes.
E

 

Hi sab,
I would try a different test meter of known specification, let's know how it goes.
E

Sure now the meter failed completely I think the 555 timer IC is taking the damage due to this defective multimeter. I should get a new proper standard meter and get a whole set of new ICs and start it over.

I will post an update after it is done.

Thanks.

 

Don't forget that a multimeter will only give you a near fully positive supply voltage output reading when it goes high for your 0.1Hz oscillator. On all the others the 50% On to Off output ratio will produce an averaged voltage on the MM of half the supply voltage! You really need an oscilloscope to see the switching waveform!

 

When I try measuring voltages between the pins for very long, it fries up the 555 timer IC and I lost 3 of them.

Hi,
Did you see this clip?
E

 

Hi sab,
I would try a different test meter of known specification, let's know how it goes.
E

I have ordered and received a new multimeter. Now I replaced all the 555 timers and when I meassure the output voltage, at 0.1 Hz board where Ra is 10kOhm, Rb is 719 kOhm and C is 10 uF the output Voltage of the 555 timer is 11.8 Volts max from OUT pin to GND when Vcc is 12 Volts. For all other frequencies the Ra, Rb, and C values I gave in post #1 it is 6 V output from 555 Timer output to GND and Vcc is 12 Volts DC.

Could someone tell me what decides the output Voltage at the OUT pin of the 555 timer. Is there any means to make all the 555 timer output voltages more or less equal.

Thanks.

 

Could someone tell me what decides the output Voltage at the OUT pin of the 555 timer. Is there any means to make all the 555 timer output voltages more or less equal.

Thanks.

Here is a snippet from the datasheet for the NE555:




I didn't see a chart on the datasheet, but using a 12v supply, the output will be about 1.5v-2v less, depending on the load current.

Make sure to use parts from a respectable vendors and manufactures.

 

Make sure to use parts from a respectable vendors and manufactures.

So the problem could be with the 555 timers I suppose. I will look into it. I have taken the Voltage readings on no load.

 

I replaced the 555 timer from the 0.1 Hz board to other boards. In 0.1 Hz it gives 11.8 Volts max and the same timer IC gives 6 Volts in all the other frequency boards.

But earlier I found some the 555 timers working strange. Initially they gave 5 to 6 Volts output but suddenly they gave 11 Volts and stayed there and sometimes they burnt out. I thought the meter was defective and it did stop working. So I got a new good meter and replaced all the timers this was the final result. Looks strange to me I tried 555 timers from 3 vendors. I am not able to find out why I get 6 Volts on all the other boards.

 

I replaced the 555 timer from the 0.1 Hz board to other boards. In 0.1 Hz it gives 11.8 Volts max and the same timer IC gives 6 Volts in all the other frequency boards.

But earlier I found some the 555 timers working strange. Initially they gave 5 to 6 Volts output but suddenly they gave 11 Volts and stayed there and sometimes they burnt out. I thought the meter was defective and it did stop working. So I got a new good meter and replaced all the timers this was the final result. Looks strange to me I tried 555 timers from 3 vendors. I am not able to find out why I get 6 Volts on all the other boards.

Are you using a BJT Timer or CMOS timer?

 

Are you using a BJT Timer or CMOS timer?

Its not CMOS its normal BJT timer.

 

hi sab,
This clip from the 555 d/s shows the High and Low output voltages, it will also depend upon the output load resistance.
E

 

hi sab,
This clip from the 555 d/s shows the High and Low output voltages, it will also depend upon the output load resistance.
E
View attachment 324860

Hi eric,
I checked it but I am getting only half of the Vcc 12 Volts which is 6 Volts at the output I have taken in on no load. On load it is 5.3 Volts.

 

hi sab,
Do you have a photo you could post showing the 555 circuitry?
E

 

hi sab,
Do you have a photo you could post showing the 555 circuitry?
E

The circuit connections on the perf board?

 

Hi,
Sometimes it is possible for you to have made a wiring error, if we see your layout photo, it will help us to diagnose any problems.
E
Photo of both faces of the perf board.

 

Hi,
Sometimes it is possible for you to have made a wiring error, if we see your layout photo, it will help us to diagnose any problems.
E
Photo of both faces of the perf board.

Ok I will make a photo and post it.

 

6 volts sounds right for the other frequencies as the the meter can only show the average voltage because of the speed of the pulses and slower response of the meter. You need to see the waveform on a scope.